Conventional refrigeration systems have two basic units--a condensing unit (compressor, condenser, receiver, control and safety devices) and an air handling unit (cooling coil, heaters, fan motor). The system must be designed to operate at a wide range of ambient temperatures, various operating temperatures/pressures and various cooling/humidity conditions. Since all system components are primarily controlled by refrigerant gas pressures, achieving effective and efficient operation under the above conditions is usually difficult or impossible. Conventional refrigeration system design which includes compressor unloading, hot gas by-pass, complex control circuits, etc. are usually ineffective, inefficient and difficult to install and maintain.